1. Technical Field
Various embodiments relate generally to an electronic device, and more particularly, to a semiconductor memory device and an operating method thereof.
2. Related Art
Semiconductor memory devices are memory devices implemented by using semiconductor materials such as silicon (Si), germanium (Ge), gallium arsenide (GaAs), indium phosphide (InP), and the like. The semiconductor memory devices are classified into volatile memory devices and nonvolatile memory devices.
The volatile memory devices are memory devices in which stored data is lost when their power supply is interrupted. The volatile memory devices include a static random access memory (SRAM), a dynamic RAM (DRAM), a synchronous DRAM (SDRAM), etc. The nonvolatile memory devices are memory devices that retain stored data even when their power supply is interrupted. The nonvolatile memory devices include a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a flash memory, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), a ferroelectric RAM (FRAM), etc. The flash memories are classified into a NOR type and a NAND type.
The flash memory devices can be classified into 2-dimensional semiconductor devices in which strings are horizontally formed on a semiconductor substrate. The flash memory devices can also be classified into 3-dimensional semiconductor devices in which strings are vertically formed on a semiconductor substrate.
3-dimensional semiconductor devices may be designed to solve the limitations of 2-dimensional semiconductor devices. These limitations may relate to the degrees of integration that can be provided by 2-dimensional semiconductor devices. As such, 3-dimensional semiconductor devices may be designed to have a plurality of strings vertically formed on a semiconductor substrate are included. The strings include a drain select transistor, memory cells, and a source select transistor, which are coupled in series between a bit line and a source line.